DE102008041809 discloses a method for operating a particle sensor. In a phase in which no measurements take place, a heater is set to a temperature to avoid particle deposition at electrodes used for particle measurement. Avoiding particle deposition can, for example, be based on thermophoresis.
Airborne particle pollution, especially particle matter size less than 2.5 μm diameter range (named “PM2.5”), is a big concern for countries like China, where the speed of industrialization stretches the boundaries of regulatory requirements.
As a consequence of increasing consumer empowerment, the demand for information about the air quality of living spaces is increasing. Especially in China, excessive PM2.5 pollution has become a common problem in the last decade. This problem is also validated by continuous measurements in various Chinese cities. The data is publicly available and can be simultaneously monitored by mobile phone applications or through the web.
Availability of this data as well as continuous national and international media attention has created strong consumer awareness about the problem.
Official outdoor air quality standards define particle matter concentration as mass concentration per unit volume (e.g. μg/m3). The average PM2.5 pollution concentration in mainland China has been calculated based on satellite data, and it has been found that the majority of the country exceeds the World Health Organization limits of 10 μg/m3, with some regions reaching and even exceeding PM2.5 concentrations of 100 μg/m3.
Standard reference measurement methods are based on measuring the mass of deposited or captured particles per air sampling volume for example using a quartz crystal microbalance, a tapered resonator, an impactor, or weighing filters and sieves. There is also a desire to detect specific chemicals within the air, in addition to (or instead of) measuring particle concentrations.
For many sensors, the operation principles result in a response to other compounds than the target compound, leading to incorrect readings when a target compound and an interfering compound are present simultaneously.
Taking an electrochemical formaldehyde sensor as example, compounds like alcohols and detergents can greatly influence the output, and these other compounds are commonly seen in real home conditions.
A known solution is to put a physical filter in front of the sensor to block suspended solids and liquids, however, over time this filter will get blocked and reduce the air flow through the sensor.